1. Field of the Invention
This invention relates to amorphous aromatic polyester copolymers having high tensile elongation at break.
2. Background
Polyarylates are known to have excellent physical properties, with the exception that they have a very low tensile elongation at break. This low tensile elongation limits their usefulness. The outstanding physical properties of polyarylates make them ideal candidates for specialty wire and cable applications, such as primary insulation for telephone exchange wire and as insulation and jacketing for plenum cable. These properties include low dissipation factor, low dielectric constant, low flammability and smoke evolution, high resistivity, high end use temperature and excellent processing behavior. However, until this invention, polyarylates have been excluded from these and other applications because of their low tensile elongation at break. Typically, the tensile elongation at break of compression molded polyarylate films is between 10 and 40%. Such low values for the tensile elongation at break leads to failure even in relatively mild bending tests.
It is known that cold drawing of crystalline polymers increases the tensile strength and tensile modulus, but tensile elongation at break is ordinarily decreased. Amorphous polymers usually break instead of cold drawing. Hot drawing of melt anisotropic, that is, liquid crystalline has been carried out (Japanese Kokai 62/255113; U.S. Pat. No. 4,734,240; and EP 232777) to increase the tensile modulus, but this drawing is always done within about 50.degree. C. of the glass transition temperature.